Hill's team are currently one point above the Exiles in 10th place in the Aviva Premiership, and he said: "We have to be very sharp in defence.
"Our attacking game is working really well and we are producing good rugby, but we will have to concentrate on our defensive play against Irish.
"Irish will be a different prospect to Northampton as they will play a lot of rugby and move the ball around.
"They are a danger because they have a lot of individuals who have the ability to beat people one on one. They have players who have a licence to run and pop up anywhere."
Warriors conceded five tries at Northampton, and Hill says that any repeat cannot be tolerated.
"We had a big inquest on Monday to find out why we went 37-3 down, because that is unacceptable," he added.
"I think some of the players were in awe of the opposition at the start, and we can't afford for that to happen again.
"London Irish will be full of confidence after getting their first win of the season last weekend, so we will have to make sure we start well."
Centre Josh Matavesi, scrum-half Jonny Arr and number eight Matt Kvesic all start for Worcester, while Irish return Sailosi Tagicakibau from centre to wing and include hooker David Paice.
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